7/23/2019 3 - The Resting Membrane Potential

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Topic 3 – The resting membrane potential (diffusion potential, Nernst equilibrium

potential)

Membrane Potentials Membrane potentials are determined by three factors:

1. 

The concentration of ions on the inside and outside of the cell;2. The permeability to those ions (conductance).

3. By the activity of electrogenic pumps (Na+ /K

+-ATPase and Ca

++ 

transport pumps) that maintain the ion concentrations across the

membrane.

Diffusion potential - Solution Equilibrium Concentration gradient and electrical charge.

The Gibbs–Donnan equilibrium:

Semi permeable membrane. Ions diffuse passively through the membrane until

equilibrium is attained. The membrane maintains both equal concentrations of ions

and electrical neutrality.Incase of impermeable anion. The net result at equilibrium is that diffusable ions

move in an unequal concentration. Resulting in electrical charge. 

Equilibrium potential for an ion+=Nernst potential 

The membrane potential that would be necessary to oppose the movement of that ion 

down its concentration gradient.

EK = -75 mV [K+]i = 150 mM[K+]o = 4 mM)

ENa = +50-60 mV[Na+]i = 20 mM

[Na+]o = 145 mM)

The resting membrane potential –

In the presence of several different ions, the equilibrium of the cell depends on the

relative permeability of the ions. For this, we use the Goldman-Hodgkin-Katz

equation:

Permeability is dependent on size of the ion, its mobility, etc.

Resting membrane potential = -10-90 mv.